The emergence of the NGN switch system separates the service from the control, and separates the transport layer and the control layer, and accessible terminals are becoming more and more diversified, a great many of soft terminals, portable intelligent NGN terminals start to be used in the soft switch network. The requirement for mobility of the terminals in the soft switch network generates naturally with the development of the miniaturization and portability of the terminals, as the core and key technology of the NGN, the soft switch system is constructed on the open packet network (mainly used in IP network), and the openness and planarity of the packet network provide convenience for the realization of the mobility of the terminals.
The terminal here, being a broad terminal concept, refers to all the terminals and access devices supported by the soft switch architecture, comprising: SIP (Session Initiation Protocol) terminal (terminal supporting the SIP protocol), H323 (protocol suite numbered as H.323 and defined by ITUT) terminal (terminal supporting H.323 protocol), MGCP (Media Gateway Control Protocol) terminal (terminal supporting MGCP protocol), H248 (protocol suite numbered as H248 and defined by ITUT) terminal (terminal supporting H248 protocol), NCS (Network-based Call Signalling) terminal (terminal supporting NCS protocol), and access devices such as IAD (Integrated Access Device).
Traditional roam technology is based on circuit and mobile network. With the development of the NGN, it is required that the terminal in the NGN network can also roam as the mobile terminal does. However, the manner for realizing the roam is required to be based on technology of IP network, which is different from the roam technology of the current mobile network. Currently, no solution is available for solving the problem.